In the context of the present text, a “dental masking compound” according to the invention is understood to mean a photopolymerizable dental composition based on radically curable acrylate/methacrylate systems for application to and for the isolation and protection of gums and/or teeth before and during dental treatment.
There are a number of treatment methods used by dentists in which aggressive chemical substances which may be harmful to health and which may damage the oral mucosa are used in the oral cavity.
For example, during placement of a composite filling, use is made of the so-called “acid etch technique” in which both the enamel and the dentin of a prepared cavity are conditioned to build up adhesion before applying a bonding liquid. The conditioning agent used may be for example phosphoric acid, maleic acid, nitric acid, citric acid or oxalic acid. Nowadays, use is generally made of a 35-40% strength phosphoric acid. In order to be able to obtain a sufficient etch pattern on the prepared enamel, the acid is first left to act on the enamel for 15 seconds and then the acid is applied to the dentin, where it is allowed to act for a further 15 seconds. Before continuing with the treatment, the acid residues are then rinsed off and removed by suction. During this process, the gums as soft tissue must be isolated from the acid residues.
The preparations are often located at the edges of the teeth or at the necks of the teeth. In these cases, the adjacent tooth and/or the soft tissue is in the direct vicinity of the treatment site. Of course, in such cases, the adjacent tooth and/or gums must be protected from the etching agent.
Another method used by dentists, in which the oral cavity comes into contact with aggressive chemical substances, is oxidative tooth whitening, also known as “bleaching”, this being a method which has in recent times become an integral part of aesthetic (cosmetic) dental treatment. The whitening effect is in this case achieved by oxidizing agents such as hydrogen peroxide, perborates or carbamide peroxide. Usually, peroxide-containing gels are used.
Enamel and dentin are stained by colorings that have become embedded in the tooth. The peroxides used penetrate into the tooth substance and oxidize the embedded colorings. Colorless fragments are left behind, and stains are removed from enamel and dentin. The reactive species in this process are free radicals which are able to attack and to destroy even the body's own structures. During the whitening of vital teeth, the bleaching agent is applied to the outer tooth surfaces as far as the area of the gingival margin. It is known from early conventional experiments that, in a high percentage of patients, gingival irritation occurred during the bleaching treatment. In order to prevent this irritation, a protective masking of the oral mucosa is necessary.
There are numerous other treatment methods used by dentists in which the treated tooth or even a plurality of treated teeth must be kept in a dry state. To this end, this treatment site must remain shielded in a liquid-tight manner from surrounding hard and soft tissue.
The conventional method for shielding and isolating tooth substance to be treated from the rest of the oral cavity and for protecting vulnerable soft tissue is the so-called “rubber dam technology” which was developed using a tensioned rubber sheet, referred to as the rubber dam. In this technique, the dentist perforates the rubber dam membrane at the appropriate points using a punch and then places the perforated membrane over the tooth to be treated. The rubber dam is then tensioned by means of a rubber dam frame, so that the tooth is shielded from the surrounding oral cavity. There are many disadvantages of the “rubber dam technology”. For instance, the patient usually experiences an unpleasant feeling due to the compressive stress of the metal brackets on the tooth. He can no longer close his mouth and has to breathe through the nose. The method is extremely complicated and time-consuming for the dentist and is also highly sensitive to errors during use. For example, if the hole is not punched to the correct size in the rubber sheet, the rubber dam will not sit precisely and in a taut enough manner along the gingival margin and will not provide sufficient sealing. There is also the risk that the sheet may tear during tensioning or during the treatment, so that the shielding effect is lost and for example aggressive chemical substances can pass unhindered to the soft tissue parts of the mouth and may cause damage there.
It is known that, during the radical polymerization of light-curable methacrylate systems, a large quantity of heat is produced and must be dissipated, particularly when such compositions are to be used for example on the soft tissue of the mouth interior. It should be ensured that no pain or even burning can occur as a result of the quantity of heat released in the oral cavity of the patient.
U.S. Pat. No. 6,305,936 B1 proposes compositions based on radically curable methacrylate systems and methods which are said to overcome the above-mentioned disadvantages of the rubber dam technique. To reduce the amount of heat, non-reactive plasticizers such as polyols or mineral oil are used in U.S. Pat. No. 6,305,936 B1. One disadvantage here is for example the fact that the use of non-reactive plasticizers disrupts the process of homogeneous crosslinking and thus may lead to the presence of unreacted monomers. Monomeric methacrylates have cytotoxic properties and may have a sensitizing effect on the tissue.
U.S. Pat. No. 6,800,671 B1 relates to isolation material for isolating tooth substance to be treated and the surrounding gums. The compositions described therein contain unsaturated, curable compounds which have an unsaturation index of at least 500. According to U.S. Pat. No. 6,800,671 B1, preferred curable compounds are dimethacrylate polyether urethane oligomers having molecular weights of between 1000 and 3000 g/mol. In addition to these multifunctionally unsaturated compounds, the compositions described therein contain a curing agent and an adhesion-promoting compound. In order to be able to ensure a workable consistency of the composition, a non-curable diluent such as for example mono-, di- or triglycerides or vegetable oil may be added to the composition of U.S. Pat. No. 6,800,671 B1.
WO 2008/096182 relates to a photopolymerizable material for isolating and for protecting the gums, for example during tooth whitening. The composition described therein comprises at least one monomer, at least one polymerization agent, at least one inert raw material and, as a further component, at least one compound having antioxidant, anti-inflammatory or sedative properties. Tocopheryl acetate, a compound which does not participate in radical polymerization, is used in a quantity of up to 25% by weight in some examples. In the case of the compositions according to WO 2008/096182, it is also to be expected that these do not form homogeneous polymers and that an excessively high quantity of unreacted monomer will be present in the cured material.
U.S. Pat. No. 5,900,245 also provides a system for shielding soft tissue, wherein the tissue surface is coated with a plastic composition. Therein, firstly a polymerization initiator is applied to the tissue surface and then a curable composition is applied to the ready-prepared tissue surface and is cured under light.
EP 1 553 915 B1 discloses the use of an elastomeric masking compound which adheres to the gums and which, as a two-component system, mixed at ambient temperature, crosslinks in a self-curing manner on the tissue to be protected. This system is based on silicone chemistry.
DE 42 33 886 C1 discloses polymerizable conditioning agents based on methacrylate and a method for pre-treating the surface of shaped bodies made from polyacrylate, polymethacrylate and polycarbonate plastics prior to application of polymerizable methacrylate material and use of the conditioning agent. The conditioning agent may contain monocyclic terpene hydrocarbon. A use of the disclosed conditioning agent for isolating tooth substance to be treated and for protecting the surrounding gums and/or one or more adjacent teeth against dental treatment agents is not described; such a use moreover appears to be ruled out due to the use of alkyl methacrylates, which are classified as toxic. DE 30 10 373 A1 discloses methods for polymerizing methacrylic acid methyl esters or mixtures thereof with further vinyl monomers in the presence of enol ethers. The polymers produced by the disclosed method are referred to as being particularly suitable for use in the dental field, for example for producing prostheses according to the powder/liquid method. Not disclosed, however, are compositions which appear to be suitable for producing a (sufficiently elastic and non-toxic) isolation of tooth substance to be treated and protection of the surrounding gums and/or one or more adjacent teeth against dental treatment agents.
DE 27 27 480 A1 discloses impact-resistant, vitreous plastic alloys of polymethacrylates and aliphatic polyurethane ureas. Methods for the production thereof are disclosed, in which use is made of monomer mixtures comprising sulfur-containing molecular weight regulators. Not disclosed are compositions for the dental field and in particular also compositions which appear to be suitable for producing a (sufficiently elastic and non-toxic) isolation of tooth substance to be treated and protection of the surrounding gums and/or one or more adjacent teeth against dental treatment agents.
DE 17 95 395 A discloses methods for producing polymers and copolymers of (meth)acrylic acid esters and acrylonitrile in the presence of polymerization catalysts and compounds having a six-membered ring containing two non-conjugated double bonds, one of which may be semicyclic (exocyclic). The specifically disclosed polymerization catalysts are thermal catalysts; photoinitiators or photopolymerizable dental compositions are not disclosed.
U.S. Pat. No. 4,490,497 A discloses compositions for surgical cement, which can be used in the production of dental prostheses. A liquid component of the composition comprises as the “chain stopper” for example a diunsaturated monocyclic terpene or a monounsaturated bicyclic terpene. Not disclosed are compositions which appear to be suitable for producing a (sufficiently elastic and non-toxic) isolation of tooth substance to be treated and protection of the surrounding gums and/or one or more adjacent teeth against dental treatment agents.
EP 1 720 506 B1 discloses a filled and polymerizable dental material and also a method for the production thereof. As use examples, the following are mentioned: tooth filling materials, core build-up materials, materials for temporary crowns and bridges, dental cement adhesives, materials for artificial teeth, veneering materials, sealing materials and dental varnish. It is disclosed that the dental material may contain additives and/or modifiers in order to set certain properties; a long list of examples includes “terpinenes”. Not disclosed, however, are compositions which appear to be suitable for producing a (sufficiently elastic and non-toxic) isolation of tooth substance to be treated and protection of the surrounding gums and/or one or more adjacent teeth against dental treatment agents.
In the systems for the radical polymerization of light-curable compounds, the problem of the considerable development of heat is in all cases tackled either by adding non-reactive additives to the composition and/or by using monomers of high molecular weight, i.e. compounds having a small number of double bonds. The use of substances which do not participate in the crosslinking on the one hand disrupts the homogeneous progress of radical polymerization and moreover, as is known, leads to the compounds not incorporated in the network from migrating out of the organic matrix and possibly damaging the soft tissue. If, on the other hand, monomers of high molecular weight are used, the mobility of the functional groups is reduced and the likelihood that each reactive group will also find an appropriate reaction partner is decreased. The mechanical properties of the protective film are diminished and the quality of the isolation material will suffer.
With the chemically curing systems based on silicone, the crucial advantages are obtained that they are biocompatible and exhibit no development of heat during curing. However, the acceptance of silicones by dentists is not very pronounced since dentists are primarily interested in rapid curing processes delivered by the use of light-curable compounds.
The object of the present invention is therefore to provide a composition for isolating tooth substance to be treated and for protecting the surrounding gums and/or one or more adjacent teeth against dental treatment agents based on light-curable methacrylate/acrylate systems, which is not reliant on the addition of non-reactive additives or the exclusive use of monomers of high molecular weight. Such a material should cure quickly, should not release any compounds not involved in the polymerization to the surrounding tissue, should exhibit high crosslinking rates and thus no longer contain, after curing of the material, any disadvantageous quantities of unreacted monomers which may subsequently have a harmful effect on the tissue, should provide a regularly constructed network and thus exhibit good mechanical properties, should adhere to the tissue and should nevertheless be easily removable.
The object is achieved by a composition according to claim 1. Advantageous embodiments of the invention are indicated in the dependent claims.
The present invention thus relates to a photopolymerizable dental composition for application to and for the isolation and protection of gums and/or teeth during dental treatment, comprising:
(a) one or more photopolymerizable monomers selected from the group consisting of acrylates and methacrylates, preferably from the group of the methacrylates,
(b) one or more photoinitiators, preferably selected from the group consisting of alpha-diketones, benzoin alkyl ethers, thioxanthones, benzophenones, acyl phosphine oxides, acetophenones, ketals, titanocenes, borates and sensitizing dyes,
(c) one or more molecular weight regulators selected from the group consisting of compounds which can be reacted with a radical of a monomer of component (a) with abstraction of an H radical from the molecular weight regulator in the allyl position,
and optionally one or more further additives.
It has surprisingly been found that it is possible to provide light-curable compounds based on photopolymerizable monomers from the group of acrylates and methacrylates in the form of masking compounds for isolating tooth substance to be treated and for protecting the surrounding gums and/or one or more adjacent teeth against dental treatment agents (in particular dental bleaching agents) if the molecular weight regulators to be used according to the invention are added to the compounds. The compositions according to the invention cure quickly, do not release any great quantities of heat to the surrounding area, exhibit high crosslinking rates, preferably do not contain any non-reactive components and preferably do not contain exclusively monomers of high molecular weight.
The compositions according to the invention preferably contain one or more photopolymerizable monomers of low molecular weight, more preferably one or more photopolymerizable monomers having a molecular weight of <700 g/mol, particularly preferably having a molecular weight of <600 g/mol.
In a further preferred embodiment, a composition according to the invention contains a total quantity of photopolymerizable monomers of low molecular weight of more than 50% by weight, relative to the total amount of monomers in a composition according to the invention.
It was surprisingly found that in particular the molecular weight regulators to be used with (particular) preference according to the invention (see below) provide a highly effective regulating effect in a dental masking compound according to the invention. The observed temperature profile of a masking compound according to the invention is reduced in its maximum by several degrees Celsius compared to the temperature development of a formulation with no molecular weight regulator. Given the presence of a suitable molecular weight regulator, the released quantity of heat is not released in an unchecked and uncontrolled manner “in one fell swoop”, but rather in a “regulated”, i.e. controlled manner, so that high thermal stresses or even burning on the tissue in the oral cavity can be ruled out. At the same time, the regulator must reduce the molecular weight of the polymer so that the material adheres well to the tissue and nevertheless is easily removable.